The Morita?Baylis?Hillman Reaction of Chiral Highly Oxygenated Cyclopent‐2‐enones

The Morita? Baylis? Hillman (MBH) reactions of (4S,5R,7R,8R)‐ and (4R,5R,7R,8R)‐4‐hydroxy‐7,8‐dimethoxy‐7,8‐dimethyl‐6,9‐dioxaspiro[4.5]dec‐2‐en‐1‐ones ( 2 and 3 , resp.) with aldehydes using various catalysts were studied. A combination of Bu₃P/phenol in THF was found being optimum conditions giving the corresponding MBH adducts with high diastereoisomeric ratios. After separation, each stereomerically pure isomer of the MBH adducts was subjected to hydrolysis employing 1% aq. CF₃COOH (TFA) in a water bath of an ultrasonic cleaner to afford the corresponding polyhydroxylated cyclopentenones in good yields.     

19-nor-11-Oxooleanan-12-ene and 18,19-seco-19-oxours-11,13(18)-diene triterpenes from Diospyros decandra bark

Four new triterpenes, 2α,3β-dihydroxy-19-nor-11-oxo-20-dimethylurs-12-en-24,28-dioic acid (equivalent to 2α,3β-dihydroxy-19-nor-11-oxoolean-12-en-24,28-dioic acid), 2α,3β-dihydroxy-18,19-seco-19-oxours-11,13(18)-dien-24,28-dioic acid, 2α,3β,19α-trihydroxy-11-oxours-12-en-24,28-dioic acid and 2α,3β,19α-trihydroxy-28-1′-β-d-[glucopyranosyl-(1″→6′)-glucopyranosyl]-urs-12-en-24,28-dioic acid were isolated from the methanol extract of the bark of Diospyros decandra as their acetate-methyl ester derivatives. The first two compounds represent the biosynthetic transformation products of 2α,3β,19-trihydroxyurs-24,28-dioic acid via oxidative rearrangement of ring E.     

A highly enantioselective Diels-Alder reaction of 1,2-dihydropyridine using a simple β-amino alcohol organocatalyst for a practical synthetic methodology of oseltamivir intermediate

An easily prepared chiral amino alcohol catalyst was found to provide an efficient synthetic intermediate of oseltamivir with excellent chemical yield and enantioselectivity (up to 98% yield and up to 98% ee) in enantioselective Diels-Alder reactions of 1,2-dihydropylidines with acroleins.     

Asymmetric synthesis of isoquinuclidines by Diels–Alder reaction of 1,2-dihydropyridine utilizing a chiral Lewis acid catalyst

The chiral isoquinuclidine derivative, 2-azabicyclo[2.2.2]octane ring system, endo-(7R)-3 was obtained in good yield with excellent diastereoselectivity (up to 92% de) by Diels–Alder reaction of 1-(phenoxycarbonyl)-1,2-dihydropyridine 1 with N-acryloyl-(4S)-4-benzyloxazolidin-2-one (4S)-2 using titanium-(2R,3R)-TADDOLate 4 as a chiral Lewis acid catalyst in toluene at 0 °C. On the other hand, endo-(7S)-3 was obtained in good yield with excellent diastereoselectivity (up to 97% de) by Diels–Alder reaction of 1 with (4R)-2 using Cu(OTf)₂/(4S,4′S)-bis(oxazoline) catalyst 8 as a chiral Lewis acid catalyst in dichloromethane at 0 °C. In these reactions, the choice of solvent and the combination of titanium-(2R,3R)-TADDOLate 4 {or Cu(II)/(4S,4′S)-bis(oxazoline) 8} and dienophile (4S)-2 {or (4R)-2} are very important. The stereochemistry of endo-(7R)-3 has been established to be (1R,4S,7R) and the reaction mechanism is proposed.     

Preparation of PMMA/acid-modified chitosan core-shell nanoparticles and their potential as gene carriers

The core-shell nanoparticles consisting of poly(methyl methacrylate) (PMMA) cores surrounded by various acid-modified chitosan shells were synthesized using a surfactant-free emulsion copolymerization, induced by a tert-butylhydroperoxide (TBHP) solution. Methyl methacrylate (MMA) was grafted onto four acid-modified chitosans (hydrochloric, lactic, aspartic, and glutamic acids) with MMA conversions up to 64%. The prepared nanoparticles had diameter ranging from 100 to 300 nm characterized by atomic force microscopy and displayed highly positive surface charges up to +77 mV. Transmission electron microscopic images clearly revealed well-defined core-shell morphology of the nanoparticles where PMMA cores were coated with acid-modified chitosan shells. The effect of acid-modified chitosans on particle size, intensity of surface charge, morphology, and thermal stability were determined systematically. The plasmid DNA/nanoparticles complexes were investigated with ζ-potential measurement. The results suggested that these nanoparticles can effectively complex with plasmid DNAs via electrostatic interaction and could be used as gene carriers.